In order to reduce the transmittance of infrared, visible and ultraviolet radiation through the window of a building or vehicle, the art has developed a variety of different products which can be adhered to planar or curved windows. The products, often referred to as solar control films or sheets, alter the solar energy transmission, reflection, and absorption of the window. The most common function is to reduce solar heat gain, thereby improving comfort and reducing cooling load within an architectural structure or a vehicle.
Many solar control films use an infrared-reflecting metal such as aluminum, copper, or silver as a thin film layer and the reflection level in the infrared wavelengths is increased in these layers, making them at least somewhat spectrally selective. However, such thin metal layers are subject to rapid oxidation under basic or acidic conditions, especially in the presence of salt. This is especially problematic if these layers have further layers applied to them using aqueous techniques. Various methods have been used to improve the performance of such layers while protecting them from oxidation.
U.S. Pat. No. 5,956,175 describes a solar control window film comprised of a transparent substrate bearing a thin, optically transparent layer of metal, an optically transparent layer of near infrared energy absorbing material and a transparent layer of protective material overlying and protecting the near infrared energy absorbing material and the metal.
U.S. Pat. No. 6,929,864 discloses a film containing first and second metal or metal alloy layers separated by a crosslinked polymeric spacing layer whose thicknesses are such that the film is extensible visible light-transmissive and infrared reflective. The film can be joined or laminated into glazing (especially non-planar vehicular safety glazing) with reduced likelihood that the metal or metal alloy layers will be damaged or distorted.
U.S. Pat. No. 7,659,002 discloses low-emissivity stacks comprising at least one absorbing layer. The low-emissivity coatings comprise, in order outward from the substrate, a first dielectric layer, a first Ag layer, a first barrier layer, a first absorbing layer, a second dielectric layer, a second Ag layer, a second absorbing layer, a third dielectric layer, and optionally, a topcoat layer. Methods are also disclosed for depositing such coatings on substrates.
U.S. Pat. No. 7,951,473 discloses optical coatings with improved durability, the coating comprising a durability enhancing layer, a nucleation layer and an infrared reflecting layer. The patent also discloses methods of making thin film layers having enhanced durability.
U.S. Pat. Publn. No. 2014/0242321, having common assignee herewith, the disclosure of which is incorporated herein by reference, discloses methods and materials for preparing bridging films. In one aspect, the bridging films are non-porous and are suitable for protecting adjacent porous films. For example, the bridging films contact a porous film and protect the porous film from transfer of gases and/or liquids into the pores of the porous film. In another example, bridging films protect the porous film from abrasion.
U.S. Pat. Publn. No. 2015/0285956 discloses methods of making a multilayer optical film. In one embodiment, the method comprises providing a multilayer optical film and disposing onto the multilayer optical film a plurality of layers deposited by layer-by-layer self-assembly of nanoparticles, polymers, and combinations thereof. The multilayer optical film typically comprises a plurality of alternating polymeric layers of a low refractive index layer and a high refractive index layer that reflects at least one bandwidth of electromagnetic radiation ranging from ultraviolet to near infrared. Multilayer optical film articles are also disclosed that comprise a plurality of layers disposed onto the multilayer optical film, wherein the plurality of layers comprises layer-by-layer self-assembled nanoparticles, polymers, and combinations thereof.
U.S. Pat. Appln. Publn. No. 2016/0168035 discloses an optical product for use in products such as window films and electronic displays, that includes a polymeric substrate and a hardcoat having a defined abrasion resistance and permeability. The hardcoat may comprise silicon oxide.
U.S. Pat. No. 5,071,206 discloses visually transparent, color corrected, infrared reflecting films for solar heat control that employ Fabry-Perot sandwich interference filters having three or more transparent layers of sputter-deposited metal such as silver directly contiguous with dielectric spacer layers and optionally boundary layers. The document acknowledges that certain prior art products of this type can exhibit a strong color cast.
Color correction has typically been imparted to optical products such as solar control films by use of organic dyes. More particularly, current commercial practice for producing dyed film from polyester involves swelling of the molecular structure of the substrate in baths of hot organic solvent such as ethylene glycol during the dyeing process, as swelled polyester (particularly PET) films are capable of absorbing organic dyes. These films and their manufacturing processes suffer many drawbacks.
Firstly, the substrates require exposure to organic solvents and elevated temperatures, which present both mechanical and chemical challenges such as environmental hazards and costs associated with storing the raw solvents and disposing of the resulting waste. Further, swelled substrates require special handling to avoid downstream stretching thereby decreasing the production yield. Next, the elevated polyester processing temperatures and residual solvents in the substrate film after drying constrain downstream use and processing of substrates which in turn limits the potential end-use applications for such dyed films. On the process side, the existing methodology uses large volume dye baths which makes rapid color change within commercial manufacturing difficult. Finally, only a limited number of organic dyes are soluble and stable in the hot solvent swelling media and many of those are subject to degradation by high energy radiation (sub 400 nm wavelength) to which the substrate is subjected when used in window film applications, thereby shortening the useful lifetime of the product.
To address these drawbacks, some film manufacturers have transitioned to using a pigmented layer on the surface of a base polymeric film for tinting a polymeric film. For example, U.S. Published Application number 2005/0019550A1 describes color-stable, pigmented optical bodies comprising a single or multiple layer core having at least one layer of an oriented thermoplastic polymer material wherein the oriented thermoplastic polymer material has dispersed within it a particulate pigment. Such products can suffer a myriad of processing and performance drawbacks. For example, layers of this type are typically applied as thin films and can employ a relatively high pigment concentration to achieve a desired tint level, particularly in automotive window films with a relatively high desired level of darkening such as those with an electromagnetic energy transmittance in the visible region (or Tvis) of less than 50%. These high pigment concentrations are difficult to uniformly disperse within the thin layer. More generally, pigmented layers can suffer from greater haze and reduced clarity even in applications (for example architectural window films) with a relatively moderate, low and even minimal levels of desired darkening.
U.S. Pat. No. 9,453,949 discloses an electromagnetic energy-absorbing optical product useful particularly for automotive and architectural window films. The electromagnetic energy-absorbing optical product includes a polymeric substrate and a composite coating that includes first and second layers, each containing a binding group component which together form a complementary binding group pair. One of the layers may be provided with an electromagnetic energy-absorbing particle which may be a pigment.
A continuing need nonetheless exists in the art for infrared-rejecting optical products that meet haze, clarity, surface uniformity, UV-stability and product longevity demands of current commercial window films as well as automotive window and vehicle coloring and/or protection films, that are resistant to oxidation, and that allow application of a pigmented coating layer capable of manufacture by an environmentally friendly, aqueous-based coloring process that may be performed at ambient temperatures and pressures.